1. Field of the Invention.
This invention relates to porous polymeric beads that have finely divided particles of activated carbon dispersed within the polymer and have biocatalytic material contained in macropores within the beads. The beads of the invention are useful in separating small quantities of organic and inorganic contaminants from solutions and are particularly efficient in removing deleterious chemicals from aqueous streams.
2. Prior Art.
U.S. Pat. No. 5,486,292, Bair and Camp, the entire disclosure of which is hereby incorporated by reference herein, provides an excellent review of known methods aimed at significantly decreasing the concentrations of various metals and dissolved organic contaminants from aqueous streams. The patent notes that several of the then known methods involved the use of bioreactors loaded with porous polymeric beads containing particular extractants. However, the polymeric beads of the then known methods had one or more of several shortcomings, such as excessive friability, insufficient rigidity, difficulty in retaining or sealing the extractant within the beads, limited capacity, limited effective life, inadequate density to avoid floating in water, excessive swelling in water etc.
The aim of the invention described in U.S. Pat. No. 5,486,292 was to provide a bioreactor in the form of polymeric beads which removes low concentrations of contaminants from streams for long periods of time. To accomplish this task, U.S. Pat. No. 5,486,292 suggests an improved bioreactor in which biocatalyst material is supported within porous synthetic organic polymer beads having activated carbon powder dispersed within the polymer of the beads and the biocatalyst material being located within macropores of the bead, the carbon powder preferably amounting to 2.3 to 7 times the weight of the polymer and the bead typically having a BET specific surface area (indicative of microporosity) of at least 400 square meters per gram, a mercury intrusion volume (indicative of macroporosity) in the range of 1.8 to 2.5 cubic centimeters per gram and a void volume of at least 40% of the total volume of the bead. Preferably, the biocatalyst is a community of bacteria, which typically are selected so that an organic chemical that is adsorbed by the activated carbon powder will be metabolized by the bacteria. Preferred polymers for the beads, and the only polymers specifically illustrated in U.S. Pat. No. 5,486,292 are aramid polymers (Nomex), selected from poly(m-phenylene isophthalamide) and copolymers thereof, and a polymer or copolymer formed from terephthalic acid, isophthalic acid, m-phenylene diamine and 2,4-diaminobenzene sulfonic acid. A method for making such beads, inoculating them with biocatalyst and using them successfully to remove contaminants from various liquid streams are disclosed in the patent. The patent suggests that activated-carbon-powder-loaded polymeric beads having substantially the same macroporosity and the same microporosity as those described and claimed in the patent would provide substantially the same favorable results in decontaminating various streams as did the specifically described activated-carbon-powder-loaded aramid polymer porous beads. However, such aramid polymers are quite expensive and manufacture of beads therefrom often involves the use of toxic organic solvents.
In view of the situation. described in the preceding paragraph, work was undertaken by the present inventors to prepare porous beads having characteristics similar to those set forth for the polymeric bioreactor beads of U.S. Pat. No. 5,486,292 from polymers other than aramids. The present inventors have found that two specific Nylon polymers could function about as well as the aramid beads disclosed in U.S. Pat. No. 5,486,292. The term Bio-Sep refers to an activated carbon loaded polymeric bead (Nylon or Nomex).
The invention provides an improved bioreactor, which includes porous polymeric beads that have finely divided particles of activated carbon dispersed within the polymer and have biocatalytic material contained in macropores within the beads. The improvement of the present invention comprises the bead polymer being poly(hexamethyleneadipamide), also known as and referred to herein as Nylon 66, or poly(caproamide), also known as and referred to herein as Nylon 6. The carbon powder typically amounts to about xc2xe to 7 times the weight of the polymer and the bead typically has a BET specific area (indicative of microporosity) of at least about 100 square meters per gram, a mercury intrusion volume (indicative of macroporosity) in the range of about 1.2 to about 2.5 cubic centimeters per gram, and a void volume of at least about 40% of the total volume of the bead.
The invention also provides an improved process for the detoxification of an aqueous waste stream containing a chemical contaminant. The process is of the type that includes the steps of (a) passing the waste stream through a bioreactor formed of porous synthetic polymer beads having macropores and micropores, activated carbon powder dispersed throughout the polymer and bacterial biocatalyst material supported with the macropores of the porous synthetic polymer beads, (b) adsorbing the organic contaminant onto the activated carbon powder particles of the bioreactor beads, (c) the bacterial biocatalyst material within the macropores of the bead metabolizing the adsorbed chemical contaminant to water, carbon dioxide, nitrogen and/or other innocuous products and thereby regenerating the adsorbent capacity of the carbon powder, and (d) discharging from the bioreactor an aqueous stream that is substantially free of the contaminant. The improvement in the process comprises the polymer of the porous bead being Nylon 66 or Nylon 6, Nylon 66 being preferred. The process of the invention is particularly useful in separating small quantities of organic contaminants from solutions and in efficiently adsorbing potentially toxic organic chemicals from aqueous streams.
While an important aspect of the present invention is the discovery that Nylon is an excellent polymer for formation of adsorbent biocatalyst porous beads, other polymers soluble in water-miscible organic solvents but substantially insoluble in water will also be usable once optimal bead-forming conditions are found. These other polymers include: polyacrylonitrile (Orlon); polyurethane; polyurethane/polyether copolymers (including Lycra); acetylated cellulosic polymers; and acetylated polyvinyl alcohols.
An important aspect of the present invention is a bioreactor comprising porous polymeric beads having finely divided particles of activated carbon powder dispersed therein and having biocatalytic material contained in macropores of the beads, the polymer being soluble in a water miscible organic solvent and substantially insoluble in water.
A more general aspect of the invention is an improved bioreactor comprising porous polymeric beads having finely divided particles of activated carbon powder dispersed therein and having biocatalytic material contained in macropores of the beads, the improvement comprising the polymer being poly(hexamethyleneadipamide) or poly(caproamide).
One important embodiment of the present invention is a bioreactor comprising porous polymeric beads having finely divided particles of activated carbon powder dispersed therein and having biocatalytic material contained in macropores of the beads, the polymer being poly(hexamethyleneadipamide) or poly(caproamide). The polymer soluble in a water miscible organic solvent is substantially insoluble in water may be, for example, at least one of polyacrylonitrile; polyurethane; polyurethane/polyether; and acetylated cellulosic polymer and acetylated polyvinyl alcohol. Generally, the carbon powder amounts to between about to between xc2xe and about 7 times the weight of the polymer when preparing the macroporous beads.
The preferred bioreactor of the present invention has a BET surface area, indicative of microporosity, of at least about 100 square meters per gram (100 m2/g). This bioreactor also has a mercury intrusion volume, indicative of macroporosity, in the range of about 1.2 to about 2.5 cubic centimeters per gram. This bioreactor also has a void volume of at least about 40% of total bead volume.
The present invention comprises an improved process for the detoxification of an aqueous waste stream containing an organic chemical contaminant, the process comprising the steps of (a) passing the waste stream through a bioreactor having porous synthetic polymer beads with macropores and micropores, activated carbon powder dispersed throughout the polymer and bacterial biocatalyst material supported within the macropores or micropores of the porous synthetic polymer beads, (b) adsorbing the organic contaminant onto the activated carbon powder particles of the bioreactor beads, (c) the bacterial biocatalyst material within the macropores of the bead metabolizing the adsorbed chemical contaminant to water, carbon dioxide, nitrogen and other innocuous products and thereby regenerates the adsorbent capacity of the activated carbon powder, and (d) discharging from the bioreactor an aqueous stream that is substantially free of the contaminant, the improvement comprising the polymer of the porous bead being poly(hexamethyleneadipamide) or poly(caproamide).
The present invention also involves an improved process for the detoxification of an aqueous waste stream containing inorganic compounds such as, e.g., ammonia, hydrogen sulfide, and nitrite salts, the process comprising the steps of (a) passing the waste stream through a bioreactor with porous synthetic polymer beads having macropores and micropores, and bacterial biocatalyst material supported within the macropores or micropores of the porous synthetic polymer beads, (b) the bacterial biocatalyst material within the macropores of the bead oxidizing the inorganic compound to innocuous products and (c) discharging from the bioreactor an aqueous stream that is substantially free of the ammonia, wherein the polymer of the porous bead is poly(hexamethyleneadipamide) or poly(caproamide). Polymer incorporated activated carbon is not needed in the case of most inorganic compounds that are not adsorbed thereon.
One important aspect of the present invention is a process for producing polymeric beads containing dispersed activated carbon particles. This process comprises forming a mixture of activated carbon particles and a polymer dissolved in a water miscible organic solvent; and extruding said mixture through at least one nozzle to form drops falling into an aqueous solution where the polymer forms porous polymeric beads containing dispersed activated carbon particles; wherein the nozzle is formed from a low surface energy material, has an orifice that at its drop forming end has an upward sloping surface to minimize or avoid excess liquid adhesion and thus micro-drop formation.